There is a conventionally known photolithographic technology for applying a fine working on a surface of an object. In addition to a semiconductor integrated circuit, recently, this technology is also applied to fabrication of a film circuit board for use in mounting of electronic parts in a tape automated bonding (TAB) technology.
However, a misalignment of a circuit pattern to be transferred will result in a mis-mounting in the case of the circuit board. For this reason, it is necessary to effect an alignment, so that an image of a pattern of a photomask is formed at a correct position. The alignment accuracy is needed to be within, for example, .+-.10 .mu.m.
The alignment in the prior art is accomplished in the following manner: First, prior to exposure, an exposure specimen having an alignment mark is placed onto a stage. Then, light from a lamp is applied through a photomask having an alignment mark to be projected. Then, both of the alignment mark on the exposure specimen and the projected image of the photomask-side alignment mark are observed by a microscope.
A photomask position adjusting mechanism is operated so that the image of the photomask-side alignment mark is aligned with the alignment mark on the exposure specimen, thereby achieving the alignment.
In order to correctly locate one frame of the film at an image plane of a projection lens, the film feeding distance is previously set, and the feeding direction is improved by a sprocket roller disposed in front of the image plane. Further, after the film has been fed by the previously set distance, the stage having a locating pin is raised relative to one frame of the film stopped, and the locating pin is fitted into a perforation in the film. The alignment relative to the image plane in a direction of the optical axis is achieved through the aid of a retaining plate for retaining one frame of the film pushed up from the below by the stage.
In this way, in the alignment in the prior art, the photomask is located at a correct position through the aid of the exposure specimen prior to starting of the operation of exposure apparatus. In operation, one frame of the film is merely located at a correct position by the feed roller. In other words, no feed-back control is carried out for the film during exposure.